New Measurements of the Ranges of Alpha-Particles from Polonium, Uranium I and Uranium II with the Wilson Chamber

The Wilson cloud chamber method of range measurement described by the author in another paper has been applied to the $\ensuremath{\alpha}$-particle ranges of polonium, uranium I, and uranium II. The polonium measurements were undertaken as a check on the method, but are in sufficiently good accord with previous results to stand alone. The range of polonium $\ensuremath{\alpha}$-particles at 0\ifmmode^\circ\else\textdegree\fi{}C and 760 mm is 3.690\ifmmode\pm\else\textpm\fi{}0.005 cm. The range of uranium I $\ensuremath{\alpha}$-particles is 2.58\ifmmode\pm\else\textpm\fi{}0.015 cm and that of uranium II $\ensuremath{\alpha}$-particles is 3.11\ifmmode\pm\else\textpm\fi{}0.01 cm. The polonium range is derived from 335 tracks while the uranium ranges are due to a total of 594 tracks. A method of separating the number-distance curves of the two uraniums is described which eliminates the uncertainty of finding the shorter range. The uranium data are in excellent agreement with the results of Laurence. This agreement is thought to be entirely fortuitous in so far as uranium I is concerned. The precision of Laurence's work is criticised.